Method and device for the quality-assuring production of a crimp

ABSTRACT

A method and a device for producing a crimp are described. A crimp blank is plastically deformed by a forming tool. In particular when the forming tool is retracted, the force which the forming tool exerts on the crimp blank as well as the distance x by which the forming tool is displaced are measured. A change in the distance x between a position at maximum force F max  and a position that for the first time is free from forces provides an indication of an elastic recovery, i.e., a spring-back, of the crimp blank. This indication represents a measure of the quality of the produced crimp.

FIELD OF THE INVENTION

The present invention relates to a method and a device for producing a crimp.

BACKGROUND INFORMATION

“Crimping” is understood to mean a joining process in which two components are joined together by plastic deformation. In particular, as the result of crimping, a crimp, i.e., a mechanical connection between a conductor and a connecting element, for example a plug or a sleeve, may be produced which is difficult to disconnect. Such a crimp may be used as an alternative to conventional connection methods such as soldering or welding, and when it is correctly produced, may ensure a reliable electrical and mechanical connection between the two crimped components. In particular, a gas-tight connection between the two components may be established by a crimp that is correctly provided, since in the plastic deformation of a crimp blank and a finely stranded line, for example, a structure may result which is largely closed off from the penetration of oxygen, and is thus internally protected from corrosion. Customarily, for producing a crimp a crimp blank, for example in the form of a plastically deformable sleeve element or plug element, is brought into contact with a second component, such as an end of a cable, to be crimped with the crimp blank. The crimp blank is subsequently plastically deformed by pressing with a suitable forming tool which has an appropriately shaped crimp shaping surface on its side facing the crimp blank, the second component generally being completely surrounded by the crimp blank and being squeezed by same. For this purpose, the forming tool is generally displaced by a distance toward the crimp blank with the aid of a forming machine until the crimp blank has been pressed and deformed with a maximum pressing force. The forming tool is subsequently displaced away from the crimp blank, so that the component which has been crimped with the crimp blank may be removed. The forming machine may, for example, be a hydraulic, pneumatic, or electric press to which the forming tool may be fastened.

During production of the crimp, care must be taken that the crimp is of high quality to be able to ensure a durable, stable mechanical, and thus electrical, connection between the crimped components. If during the crimping, for example, a sufficient pressing force is not exerted or unsuitable contact materials are used, finely stranded lines, for example, may be insufficiently pressed to ensure a durable connection. It is thus possible for oxygen to be present at the individual lines, and for an increased contact resistance to develop between the lines and a crimp sleeve due to oxidation. There is also the risk that an incompletely pressed line may be pulled from the crimp. On the other hand, during crimping the pressing must not be too great, or the pressing must not be carried out with a forming tool that is too small, since for solid, finely stranded lines, for example, the cross sections may be excessively reduced, so that the resistance could increase to impermissibly high levels. In addition, when the pressing force for finely stranded lines is greatly exceeded, there is a risk that individual conductors may be sheared off. Furthermore, the crimp may also be damaged by fissures or breaks. As a rule, quality assurance of a crimp connection is conventionally carried out by measuring external dimensions of the crimp, by visually assessing the micrograph, for example through the center of a crimp perpendicular to the lines, and/or by force-displacement monitoring during the crimping.

SUMMARY

An object of the present invention is to provide a method for producing a high-quality crimp, and a device that is suitable for carrying out the method.

It has been found that an internal mechanical pressing state may be necessary for a reliable crimp connection. Since high-strength materials are usually used for contacts, and thus for crimps, it may be advantageous to measure the spring-back of the crimp. The spring-back reduces an internal compressive stress until a possibly pretension-free connection results. For stable electrical connections, the internal pretensioning should be greater than a relaxation of the materials due to natural aging during the useful life of the crimp.

To ensure consistent quality, it may be advantageous to directly measure a spring-back travel of the crimp during its production. This may provide a direct conclusion as to the internal pretensioning state.

The position of the forming tool at maximum crimping force may be ascertained for measuring the spring-back travel. This maximum crimping force is generally present directly at the reversal point of a travel of the forming tool. In addition, the position of the forming tool may be ascertained as soon as it leaves the crimp blank, i.e., when it is practically free of force. The difference in these two positions indicates the spring-back travel of the crimp.

This information concerning the spring-back travel thus ensures an indication of quality for almost all possible defects of a crimp, including possible material defects of the crimp. Other possible errors, such as occurrences of friction, may be reduced by correction factors.

According to one aspect of the present invention, it is proposed during the production of a crimp to measure a force exerted by the forming tool on the crimp blank on the return path, i.e., after a maximum pressing force effectuated by the forming tool has been reached and the forming tool is then displaced away from the crimp blank. In addition, a minimum return path length by which the forming tool is displaced on the return path between the state having the maximum pressing force and a state that is essentially free of pressing forces should be determined In other words, a distance should be determined between a position in which the fowling tool presses onto the crimp blank with the maximum pressing force, and a position which the forming tool reaches when it is subsequently displaced away from the crimp blank, and at which for the first time essentially no pressing force is exerted on the crimp blank by the forming tool.

In this regard, “essentially free of pressing forces” may be understood to mean that any forces exerted on the crimp blank by the forming tool, compared to forces which are necessary for the plastic deformation of the crimp blank, are negligible. In particular, “essentially free of pressing forces” may be understood to mean that a pressing force exerted on the crimp blank by the forming tool should be less than forces which are empirically exerted on the forming tool by the crimp blank as the result of spring-back during the displacement of the forming tool on the return path.

By determining the return path length, it may be ascertained how intensely the crimp blank springs back after the actual crimping process, i.e., after the maximum pressing force is reached.

The information concerning the return path length, and thus information concerning the spring-back of the produced crimp, may be subsequently output. It has turned out that such information may provide a good indicator of the quality of the produced crimp. A small spring-back, i.e., a short return path length, indicates a high mechanical internal pressing of the crimp, and thus also ensures high electrical quality of the crimp. A large spring-back, i.e., a long return path length, indicates problems in the production of the crimp or of the contact thus established, and may thus indicate insufficient quality of the crimp and/or low electrical stability of the crimp.

The proposed method results in an option to obtain a reliable measure of the quality of the crimp directly during production of the crimp. In particular, such quality may be ascertained nondestructively, quickly, and cost-effectively, for example directly during the crimping process.

The return path length to be determined may be ascertained by measuring a distance between a first reference point, which correlates with the position of the crimp blank, and a second reference point which correlates with the position of the forming tool. For example, the crimp blank may be accommodated in a crimp blank holder in which it is held and optionally shaped during the crimping process. For example, a suitable reference point may be defined on the crimp blank holder which correlates with the position of the crimp blank. A reference position on the forming tool, preferably in the vicinity of the crimp shaping surface, may be defined as a second reference point. Since the distance between the two defined reference points progressively increases during the displacement of the forming tool on the return path of the forming tool away from the crimp blank, by measuring the distance between the two reference points on the one hand at a point in time when the tool exerts the maximum pressing force on the crimp blank, and on the other hand at a point in time when the forming tool for the first time no longer exerts force on the crimp blank, the return path length to be determined may be ascertained.

For the case, for example, that the position of a crimp blank holder is fixed and its deformation under the pressing force is known, and therefore a first reference point may be assumed to be fixed, using a position measuring device it may be sufficient to measure only the position of the forming tool or of a second reference point that correlates with the position of the forming tool or its crimp shaping surface. In this regard it may be advantageous to select the second reference point to be as close as possible to the crimp shaping surface, which during the crimping process plastically deforms the crimp blank. It may thus be ensured that by measuring the return path length, the actual spring-back travel of the deformed crimp blank, situated between the crimp blank holder and the crimp shaping surface, is determined, and that influences such as a deformation of the forming tool or of a machine which moves the forming tool may be largely eliminated.

The return path length is preferably measured in a contactless manner In particular, the distance between the two defined reference points may be optically measured, for example with the aid of a laser distance measuring device. Such a laser distance measuring device may be designed to emit a laser beam from one of the reference points to the other reference point, and to redetect a portion of the laser light reflected from that location, to be able to obtain information concerning the distance between the two reference points on the basis of a propagation time measurement. The contactless measurement of the return path length may allow a reliable, wear-free determination of the quality of the crimp. In particular an optical measurement, for example with the aid of the laser distance measuring device, allows a very accurate determination of the return path length, for example with an accuracy in the range of a few microns. A precise indication of the spring-back travel during the production of the crimp, and thus of the quality of the produced crimp, may thus be obtained in a simple, reliable, and wear-free manner.

It is pointed out that possible features and advantages of the described present invention are described herein in part with reference to the proposed method for producing a crimp, and in part with reference to a device for producing a crimp. Upon study of the description, those skilled in the art will recognize that the described features in each case may be combined with one another, and that further synergy effects may be achieved by such combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a device for carrying out a crimping process according to one specific embodiment of the present invention.

FIG. 2 shows a typical curve of pressing forces during a crimping process.

The figures are purely schematic, and are not to scale.

DETAILED DESCRIPTION

A device is described below with reference to FIGS. 1 and 2, with the aid of which a method for producing a crimp may be carried out according to one specific embodiment of the present invention.

FIG. 1 illustrates a device 1 with the aid of which a crimp blank 3 may be crimped. Device 1 has a forming tool 5 in the form of a punch, and a crimp blank holder 7 in the form of an anvil. Forming tool 5 is fastened to a fowling machine 9, which is illustrated purely schematically. Forming machine 9 may move forming tool 5 back and forth in the vertical direction, as indicated by arrows 11, 13. Forming tool 5 has a crimp shaping surface 15 at its lower side facing crimp blank holder 7 which specifies the contour into which the crimp blank is to be plastically deformed during the crimping.

Forming machine 9 is designed to measure with the aid of a force measuring device 19 the force with which forming tool 5 is pressed against crimp blank 3 during the crimping process, and to transmit corresponding measured data to an evaluation electronics system 17.

In addition, a position measuring device 21 is provided for device 1, with the aid of which the position of forming tool 5 may be measured. In the illustrated example, position measuring device 21 is implemented with the aid of a laser distance measuring device 23 which is fixedly mounted to crimp blank holder 7. Laser distance measuring device 23 emits a schematically illustrated time-modulated laser beam 27 in a direction that corresponds to direction of motion 11, 13 of forming tool 5 during the crimping process. Laser beam 27 is reflected on a reflector 25 which is mounted at a lower end of forming tool 5 in the vicinity of crimp shaping surface 15, protruding at the side. The reflected portion of laser beam 27 is subsequently detected by a detector of position measuring device 23. Based on a phase shift to be measured between the emitted modulated laser light and the detected reflected laser light, distance x between laser distance measuring device 23 and reflector 25 may be deduced via a propagation time measurement. Laser distance measuring device 23 thus allows the position of crimp shaping surface 15 of forming tool 5 to be determined very accurately during the crimping process. Appropriate information is relayed to evaluation electronics system 17.

In the method for producing the crimp, undeformed crimp blank 3 is initially arranged on crimp blank holder 7. In this undeformed state, crimp blank 3 has two brackets 29, 31, which together with a base 33 of crimp blank 3 essentially enclose a space 35. Crimp blank 3 may, for example, be an end of a plug or a socket to which a cable is to be fastened by crimping. The cable or the plurality of exposed strands 37 of the cable may then be inserted into space 35.

During the crimping process, forming tool 5 is now progressively displaced vertically downwardly in the direction of arrow 11 by forming machine 9. Crimp shaping surface 15 comes into contact with brackets 29, 31 and deforms same as forming tool 5 moves further downwardly. A deformation which is largely plastic takes place in this initial stage. As forming tool 5 moves further downwardly, brackets 29, 31 are pressed increasingly intensely onto strands 37 present in space 35, so that on the one hand the strands are situated close to one another, and on the other hand the material of brackets 29, 31 flows in a partially plastic manner into the spaces between strands 37. The deformation of crimp blank 3, including strands 37 accommodated therein, occurs in a partially plastic manner and in a partially elastic manner

Force F exerted on crimp blank 3 by forming tool 5 is continuously measured during the progressive downward displacement of forming tool 5. The magnitude of the force is not crucial for these measurements; only the points of maximum pressing force and minimum pressing force are to be ascertained. To avoid possible error effects due to deformations of the forming machine and/or of the forming tool, the measuring device should be placed close to the crimp blank. For example, laser distance measuring device 23 may advantageously be mounted close to the support surface of the crimp blank on crimp blank holder 7, and reflector 25 used as a counterpart may be mounted, for example, in the vicinity of crimp shaping surface 15 on forming tool 5.

During the crimping process, forming tool 5 is displaced vertically downwardly until force measuring device 19 indicates that the force with which forming tool 5 presses on crimp blank 3 corresponds to a maximum pressing force F_(max). After a defined approach path, the forming tool moves upwardly until it leaves the crimp blank.

Curve 39 in FIG. 2 illustrates a typical progression of exerted pressing force F as a function of downward displacement x. During deformation of the crimp blank, pressing force F slowly increases during the plastic, elastic deformation of crimp blank 3, and upon further displacement arrives at an area in which the pressing force rises at an increasingly higher rate with the displacement. This may be regarded as an indicator that, in addition to the plastic deformation, an elastic deformation of crimp blank 3 together with strands 37 accommodated therein takes place with an increasingly greater contribution. The downward movement of forming tool 5 is terminated when maximum pressing force F_(max) is reached.

Forming tool 5 is subsequently moved vertically upwardly, as indicated in FIG. 1 by arrow 13, in order to be displaced away from crimp blank 3 on a return path. Also during this return path, force F exerted on crimp blank 3 by forming tool 5 is continuously measured with the aid of force measuring device 19.

As illustrated in FIG. 2 by curve 41, force F decreases approximately linearly over the return path as a function of displacement Ax. This may be explained in that, during the raising of forming tool 5, the elastic portion of the deformation of crimp blank 3 is once again progressively relaxed. As soon as the elastic deformation has completely diminished, crimp blank 3 no longer exerts any force on forming tool 5, which may thus be displaced upwardly, essentially free of pressing forces.

During the displacement of forming tool 5, distance x between laser distance measuring device 23 and reflector 25 is continuously measured with the aid of position measuring device 21. In particular, distance x_(max) is measured at the instant at which forming tool 5 exerts maximum pressing force F_(max) on crimp blank 3. In addition, distance x₀ is measured at which the force exerted on crimp blank 3 by forming tool 5 during the return path for the first time is at least essentially zero. Travel difference Δx=x_(max)−x₀ indicates information concerning the elastic deformation of the crimp blank, i.e., the spring-back of the crimp blank during the retraction of forming tool 5.

This information Δx represents an indicator of the quality of the produced crimp. The smaller the value of Δx, i.e., the less the spring-back, the better the general quality of the crimp. In particular when Δx deviates from otherwise ascertained values for a certain crimp, this may be an indicator of production defects.

As a result of the described method and the device which makes this method possible, a crimping process may be directly monitored, and a quality of the produced crimp may be easily and reliably analyzed based on the ascertained force-displacement diagram. 

1.-10. (canceled)
 11. A method for producing a crimp, comprising: providing a crimp blank; plastically deforming the crimp blank by pressing with a forming tool; during the pressing, displacing the forming tool by an approach path in a direction of the crimp blank with the aid of a forming machine until the crimp blank is pressed with a maximum pressing force; subsequently displacing the forming tool by a return path away from the crimp blank; measuring a pressing force exerted on the crimp blank by the forming tool on the return path; and measuring a return path length by which the forming tool is to be displaced on the return path between a state having the maximum pressing force and a state that is free of pressing forces.
 12. The method as recited in claim 11, further comprising: determining the return path length by measuring a distance between a first reference point that correlates with a position of the crimp blank and a second reference point that correlates with a position of the forming tool.
 13. The method as recited in claim 12, wherein the second reference point correlates with a position of a crimp shaping surface of the forming tool.
 14. The method as recited in claim 11, wherein the return path length is measured in a contactless manner.
 15. The method as recited in claim 11, wherein the return path length is optically measured.
 16. The method as recited in claim 12, further comprising: outputting information concerning a quality of the crimp on the basis of the determined return path length.
 17. A device for producing a crimp, comprising: an arrangement for providing a crimp blank; an arrangement for plastically deforming the crimp blank by a pressing operation; an arrangement for, during the pressing, displacing the forming tool by an approach path in a direction of the crimp blank with the aid of a forming machine until the crimp blank is pressed with a maximum pressing force; an arrangement for subsequently displacing the forming tool by a return path away from the crimp blank; an arrangement for measuring a pressing force exerted on the crimp blank by the forming tool on the return path; and an arrangement for measuring a return path length by which the forming tool is to be displaced on the return path between a state having the maximum pressing force and a state that is free of pressing forces.
 18. The device as recited in claim 17, wherein: the arrangement for plastically deforming the crimp blank includes a forming tool for plastically deforming the crimp blank, and the arrangement for measuring includes a force measuring device for measuring the pressing force exerted on the crimp blank by the forming tool, the device further comprising: a crimp blank holder for accommodating the crimp blank, and a position measuring device for measuring a position of the forming tool.
 19. The device as recited in claim 18, wherein: the position measuring device measures a distance between a first reference point that correlates with a position of the crimp blank holder and a second reference point that correlates with a position of the forming tool.
 20. The device as recited in claim 18, wherein the position measuring device includes a laser distance measuring device. 